​US aircraft, including F-22s, F-35s, and B-1s, on Monday began a massive exercise alongside South Korean forces, a move North Korean officials say brings the countries to the “brink of nuclear war.”

Exercise Vigilant Ace 18 runs from Monday to Friday, and includes 12,000 US personnel along with airmen with the Republic of Korea Air Force. The “realistic air combat exercise” also includes US Marine Corps and US Navy personnel, with a total of 230 aircraft at eight locations, according to Pacific Air Forces. The aircraft include F-22s, F-35s, F-16s, F-15s, B-1s, F-18s, E/A-18s, and F-4s.

“The threat here on the peninsula is very real, and countering that threat needs to be in the forefront of our minds,” 51st Fighter Wing Commander Col. William Betts said in a release. “My biggest expectation for the wing is to remove any ‘exercise’ mindset from the equation and maximize the realism of every response. We will ensure we have no regrets if we find ourselves executing contingency operations.”

North Korean officials called the exercise a “ceaseless large-scale war game” that is “creating a situation that a nuclear war may break out at any moment,” according to CNN.

The tensions on the Korean Peninsula have risen to the point that Sen. Lindsey Graham (R-S.C.), on Sunday, called on the Pentagon to not send any more dependents to South Korea.

“It’s crazy to send thousands of children to South Korea, given the provocation of North Korea,” Graham said on CBS’s Face the Nation. “So, I want them to stop sending dependents, and I think it’s now time to start moving American dependents out of South Korea.”